Pneumatic tire having excellent steering stability

ABSTRACT

A pneumatic tire has a block pattern of a tread defined by a plurality of circumferential grooves extending in a circumferential direction of the tread and a plurality of lateral grooves each extending across the circumferential grooves and tread ends, wherein specified chamfered face, sipe or fine groove is formed in each block of all block rows to improve a self-aligning torque in the high-speed running of a vehicle.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a pneumatic tire having particularly animproved steering stability in the high-speed running of a vehicle byincreasing a self-aligning torque of the tire.

[0003] 2. Description of Related Art

[0004] In the running of the vehicle, the steering stability is largelyaffected by disturbances such as road surface state, wind and the like,which becomes serious as the vehicle speed is increased. In theconventional pneumatic tire, however, examinations on the shape of theblock, formation of sipe and the like are not made for sufficientlysatisfying the steering stability in the high-speed running of thevehicle.

SUMMARY OF THE INVENTION

[0005] It is, therefore, an object of the invention to provide pneumatictires advantageously improving the steering stability in the high-speedrunning by directly increasing self-aligning torque of the tire throughblock, sipe and the like as a result of various studies with respect tothe block shape and formation of sipe or fine groove therein.

[0006] According to a first aspect of the invention, there is theprovision of in a pneumatic tire having a block pattern of a treaddefined by a plurality of circumferential grooves extending in acircumferential direction of the tread and a plurality of lateralgrooves each extending across the circumferential grooves and treadends, the improvement wherein each block in an outermost block row in awidthwise direction is provided on its leading edge portion with achamfered face gradually decreasing a height of the block toward aleading edge, and each block in the other block rows is provided on itstrailing edge portion with a chamfered face gradually decreasing aheight of the block toward a trailing edge, and a length of a chamferedface forming region is not more than ⅓ of a circumferential length ofthe block.

[0007] When a slip angle is applied to this pneumatic tire, the block inthe outermost block row located opposite to the applying direction ofthe slip angle contacts with ground at a large area under a largeloading and hence a force in a forward direction produced in the leadingof the block is weakened by the chamfered face formed on the leadingedge portion of the block to relatively create a large force backward toa forward rotating direction of the tire as compared with the block ofthe other block row provided on the trailing edge portion with thechamfered face, whereby restoring moment or self-aligning torque iscaused in the ground contact region of the tread. As a result, even whenthe tire is subjected to disturbance or the like, it is possible tosmoothly and rapidly return the tire in a running direction of thevehicle. Therefore, the excellent steering stability can be realizedeven in the high-speed running of the vehicle.

[0008] In a preferable embodiment of the first aspect, the chamferedface is formed in a region corresponding to not more than ⅓ of thecircumferential length of the block, preferably not less than {fraction(1/10)} thereof, whereby the ground contact area of the block issufficiently ensured.

[0009] When the length of the chamfered face forming region exceeds ⅓ ofa circumferential length of the block, the ground contact area of theblock lowers and hence cornering power important for improving thesteering stability is lacking, while when it is less than {fraction(1/10)}, the effect by the formation of the chamfered face is actuallypoor.

[0010] In another preferable embodiment of the first aspect, a height ofthe chamfered face forming region is not more than ⅓ of a height of theblock, preferably not less than {fraction (1/10)} thereof. In this case,a big self-aligning torque can be created to effectively ensure theimprovement of the steering stability during the high-speed running.When the height exceeds ⅓, the ground contact area is decreased too muchand hence the cornering power is decreased to cause a fear of degradingthe steering stability, while when it is less than {fraction (1/10)},the actual effect is lacking.

[0011] In the other preferable embodiment of the first aspect, thechamfered face is a curved face convexly extending outward in a radialdirection of the tire. In this case, the ground contact pressure isuniformized to control the lowering of the cornering power as comparedwith the case of forming a flat chamfered face or the like.

[0012] According to a second aspect of the invention, there is theprovision of in a pneumatic tire having a block pattern of a treaddefined by a plurality of circumferential grooves extending in acircumferential direction of the tread and a plurality of lateralgrooves each extending across the circumferential grooves and treadends, the improvement wherein a plurality of sipes each extending in awidthwise direction of the tread and being symmetry with respect to aline segment passing through a center of the block in thecircumferential direction of the tread are formed in each block of theblock rows so as to gradually change lengths of these sipes from an endof the block in the circumferential direction toward the other endthereof, and the sipes in each block of an outermost block row becomelong at a leading side of the block and short at a trailing sidethereof, and the sipes in each block of the other block rows become longat a trailing side of the block and short at a leading side thereof.

[0013] In this tire, each sipe formed in each block and extending in thewidthwise direction of the tread can naturally develop an excellentwater film cutting performance under its edge action but alsoparticularly decreases a block rigidity at the leading edge portion ineach block of the outermost block row. As a result, when a slip angle isapplied to the tire, a force in a forward direction produced in theleading of the block is decreased to relatively increase a force in abackward direction, while a block rigidity at a trailing edge portion isdecreased in each block of the other block rows to relatively increase aforce in a forward direction. Even in this case, the self-aligningtorque can effectively be increased based on force couple in the groundcontact region of the tread, whereby the excellent steering stabilitycan be realized during the high-speed running of the vehicle.

[0014] In a preferable embodiment of the second aspect, both ends ofeach sipe in each block are terminated in the block, whereby theexcessive lowering of the block rigidity is prevented to control theoccurrence of uneven wear.

[0015] According to a third aspect of the invention, there is theprovision of in a pneumatic tire having a block pattern of a treaddefined by a plurality of circumferential grooves extending in acircumferential direction of the tread and a plurality of lateralgrooves each extending across the circumferential grooves and treadends, the improvement wherein each block in all block rows is providedwith a single fine groove extending in a widthwise direction of thetread across the block, and the fine groove formed in each block of anoutermost block row is located in a leading edge portion of the blockand the fine groove formed in each block of the other block rows islocated in a trailing edge portion of the block.

[0016] Even in this tire, a block rigidity in each block of theoutermost block row is lower at the leading edge portion than at thetrailing edge portion, while a block rigidity in each block of the otherblock rows is lower at the trailing edge portion than at the leadingedge portion, so that the self-aligning torque can be increased to bringabout the improvement of the steering stability during the high-speedrunning likewise the previously mentioned tires.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will be described with reference to theaccompanying drawings, wherein:

[0018]FIG. 1a is a schematically partial developed view of a firstembodiment of the tread pattern according to the invention;

[0019]FIG. 1b is a diagrammatically section view of a block taken alonga line Ib-Ib of FIG. 1;

[0020]FIG. 1c is a diagrammatically section view of a block taken alonga line Ic-Ic of FIG. 1;

[0021]FIG. 2 is a schematically partial developed view of a secondembodiment of the tread pattern according to the invention; and

[0022]FIG. 3 is a schematically partial developed view of a thirdembodiment of the tread pattern according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0023] In FIG. 1 is shown a first embodiment of the tread patternaccording to the invention, wherein FIG. 1a is a schematically partialdeveloped view of the tread pattern, and FIGS. 1b and 1 c arediagrammatically section views of blocks in a circumferential directionof the tread taken along lines Ib-Ib and Ic-Ic, respectively.

[0024] Moreover, an inner structure of the tire is the same as in thegenerally used radial tire. Such an inner structure itself is notdirectly related to the invention, so that the illustration of the innerstructure is omitted.

[0025] In the illustrated embodiment, a center block row 4 located on anequator of the tire, shoulder block rows 5 located at both outermostsides of a tread portion and middle block rows 6 located between thecenter block row and the shoulder block row are defined on a surface ofa tread by four circumferential grooves 1, 2 extending straightforwardin a circumferential direction of the tread and symmetrically locatedwith respect to the equator of the tire, both tread side ends E and aplurality of lateral main grooves 3 extending across thesecircumferential grooves 1, 2 and substantially in a directionperpendicular thereto.

[0026] When such a tread portion is rotated upward as shown by an arrowA in FIG. 1a, a chamfered face 8 is formed on a leading edge portion ofeach shoulder block 7 in the shoulder block row 5 so as to graduallydecrease a height of the block toward a leading edge 7 a as seen from asection view of FIG. 1b, wherein a length 1 of a forming region for thechamfered face 8 is made not more than ⅓of a circumferential length L ofthe shoulder block 7. Preferably, the chamfered face 8 is a curved faceconvexly extending outward in a radial direction of the tire.

[0027] Furthermore, it is favorable that a height h of the formingregion for the chamfered face 8 is made not more than ⅓ of a height H ofthe shoulder block 7, whereby it is possible to effectively ensure theimprovement of the steering stability as previously mentioned.

[0028] In blocks 9, 10 of the other block rows 4, 6, as shown in FIG. 1cillustrating a center block 9, a chamfered face 11 is formed on atrailing edge portion of the block so as to gradually decrease a heightof the block toward a trailing edge 9 a, wherein a forming region forthe chamfered face 11 is made not more than ⅓ of a circumferentiallength of the block 9 likewise the above case. This is true in eachblock 10 of the middle block row 6.

[0029] Even in this case, the chamfered face 11 is favorable to be acurved face convexly extending outward in the radial direction of thetire and a height of a forming region therefor is favorable to be notmore than ⅓ of a block height.

[0030] When the blocks 7, 9 and 10 are chamfered as mentioned above, ifa certain slip angle is applied to the tire, the blocks 7 strongly andlargely contact with ground at a side opposite to the slip angle appliedside as compared with the blocks 9, 11 mainly based on a relativedifference between the forming positions of the chamfered faces 8, 11 inthe blocks, whereby the self-aligning torque of the tire canadvantageously be increased.

[0031] In FIG. 2 is shown a second embodiment of the tread patternaccording to the invention, wherein a center block row 4 located on anequator of the tire, shoulder block rows 5 located at both outermostsides of a tread portion and middle block rows 6 located between thecenter block row and the shoulder block row are defined on a surface ofa tread by four circumferential grooves 1, 2 extending straightforwardin a circumferential direction of the tread and symmetrically locatedwith respect to the equator of the tire, both tread side ends E and aplurality of lateral main grooves 3 extending across thesecircumferential grooves 1, 2 and substantially in a directionperpendicular thereto likewise the case of FIG. 1 and a plurality ofsipes 12 each extending in a widthwise direction of the tread and beingsymmetry with respect to a line segment passing through a center of theblock in the circumferential direction of the tread are formed in eachof the blocks 7, 9, 10 so as to gradually change lengths of these sipesfrom an end of the block in the circumferential direction toward theother end thereof. The sipes 12 in the shoulder block 7 become long at aleading side of the block 7 and short at a trailing side thereof, andthe sipes 12 in each of the center blocks 9 and middle blocks 10 becomelonger at a trailing side of the block than at a leading side thereof.

[0032] In the illustrated embodiment, both ends of all sipes 12 in eachblock are terminated in the block.

[0033] Moreover, the term “sipe” used herein means a narrow groovehaving generally an opening width of about 0.2-0.4 mm, wherein opposedgroove walls of the sipe contact with each other in a ground contactregion during the running of the tire under loading.

[0034] When a certain slip angle is applied to this tire, forcedirecting backward in a running direction of the tire is created in theshoulder block 7 subjected to a large load based on the difference ofthe extending lengths of the sipes 12 between mutual blocks to causecouple force in the ground contact region of the tread, whereby theincrease of the self-aligning torque in the tire can be realized.

[0035] In FIG. 3 is shown a third embodiment of the tread patternaccording to the invention, wherein each of the blocks 7, 9, 10 in allthe block rows 4, 5, 6 formed by the same method as in the first andsecond embodiments is provided with a single fine groove 13 extending ina widthwise direction of the tread across the block. The formingposition of the fine groove 13 is a leading edge portion in the shoulderblock 7 and a trailing edge portion in the other blocks 9, 10.

[0036] The term “fine groove” used herein means a groove having anopening width of about 0.5-3 mm.

[0037] Moreover, it is favorable that the fine groove 13 is locatedapart from an edge of the block near to the fine groove within a rangeof 0.1-0.35 times the length of the block in the circumferentialdirection for simultaneously establishing the steering stability and theresistance to uneven wear.

[0038] According to this tire, the increase of the self-aligning torquecan be attained under substantially the same function of the blocks asshown in FIG. 2 based on the difference of the fine groove formingposition between the mutual blocks.

[0039] The following examples are given in illustration of the inventionand are not intended as limitations thereof.

EXAMPLE 1

[0040] There is provided a pneumatic tire having a tire size of195/60R15 88H and a tread pattern shown in FIG. 1a, wherein a belt iscomprised of two cross belt layers, cords of which layers are crossedwith each other at a cord angle of 20° with respect to an equator of thetire and has a width of about 150 mm, and each block has a height of 5mm and a length in circumferential direction L of 18.9 mm, and achamfered face formed in a shoulder block has a forming region length 1of 6 mm and a forming region height h of 1.2 mm. This tire is mountedonto a rim of 6J and inflated under an air pressure of 220 kPa androtated on a drum testing machine at a speed of 60 km/h under a load of4067 N while applying a slip angle of 3° to measure a self-aligningtorque.

[0041] For the comparison, there is provided a comparative tire whereinthe chamfered face formed in all of the blocks is the same as formed inthe center block and the middle block shown in FIG. 1. The self-aligningtorque of this comparative tire is measured in the same manner asmentioned above.

[0042] When the self-aligning torque is represented by an index on thebasis that the comparative tire is 100, the index value of the exampletire is 101, so that the self-aligning torque can be increased by about1%.

EXAMPLE 2

[0043] There is provided a tire having the same structure as in Example1 except that the tire has a tread pattern shown in FIG. 2, wherein foursipes having an opening width of 0.3 mm are formed in each of all blocksand lengths of the sipes in each of shoulder blocks located at aposition apart from a tread end within 0.15 times a ground contact widthof a tread successively change into 20 mm, 14 mm, 8 mm and 4 mm from aleading edge of the block and lengths of the sipes formed in the otherblocks successively change into 20 mm, 14 mm, 8 mm and 4 mm from atrailing edge of the block. The self-aligning torque of this tire ismeasured in the same manner as in Example 1.

[0044] For the comparison, there is provided a comparative tire whereinfour sipes having a length of 10 mm are formed in all of the blocks.

[0045] When the self-aligning torque is represented by an index on thebasis that the comparative tire is 100, the index value of the exampletire is 100.5, so that the self-aligning torque can be increased byabout 0.5%.

EXAMPLE 3

[0046] There is provided a tire having the same structure as in Example1 except that the tire has a tread pattern shown in FIG. 3, wherein eachof all the blocks is provided with a fine groove having an opening widthof 2 mm and the fine groove formed in the shoulder block is locatedapart from a leading edge of the block by ⅕ of a length of the block ina circumferential direction and the fine groove formed in the otherblocks is located apart from a trailing edge of the block by ⅕ of alength of the block in the circumferential direction.

[0047] For the comparison, there is provided a comparative tire whereinthe fine groove formed in all the blocks is located in a positioncorresponding to ½ of the length of the block in the circumferentialdirection.

[0048] When the self-aligning torque is represented by an index on thebasis that the comparative tire is 100, the index value of the exampletire is 101, so that the self-aligning torque can be increased by about1%.

[0049] As mentioned above, according to the invention, the self-aligningtorque of the tire can effectively be increased to advantageouslyimprove the steering stability in the high-speed running of the vehicle.

What is claimed is:
 1. In a pneumatic tire having a block pattern of atread defined by a plurality of circumferential grooves extending in acircumferential direction of the tread and a plurality of lateralgrooves each extending across the circumferential grooves and treadends, the improvement wherein each block in an outermost block row in awidthwise direction is provided on its leading edge portion with achamfered face gradually decreasing a height of the block toward aleading edge, and each block in the other block rows is provided on itstrailing edge portion with a chamfered face gradually decreasing aheight of the block toward a trailing edge, and a length of a chamferedface forming region is not more than ⅓ of a circumferential length ofthe block.
 2. A pneumatic tire according to claim 1, wherein a height ofthe chamfered face forming region is not more than ⅓ of a height of theblock.
 3. A pneumatic tire according to claim 1, wherein the chamferedface is a curved face convexly extending outward in a radial directionof the tire.
 4. In a pneumatic tire having a block pattern of a treaddefined by a plurality of circumferential grooves extending in acircumferential direction of the tread and a plurality of lateralgrooves each extending across the circumferential grooves and treadends, the improvement wherein a plurality of sipes each extending in awidthwise direction of the tread and being symmetry with respect to aline segment passing through a center of the block in thecircumferential direction of the tread are formed in each block of theblock rows so as to gradually change lengths of these sipes from an endof the block in the circumferential direction toward the other endthereof, and the sipes in each block of an outermost block row becomelong at a leading side of the block and short at a trailing sidethereof, and the sipes in each block of the other block rows become longat a trailing side of the block and short at a leading side thereof. 5.A pneumatic tire according to claim 4, wherein both ends of each sipe ineach block are terminated in the block.
 6. In a pneumatic tire having ablock pattern of a tread defined by a plurality of circumferentialgrooves extending in a circumferential direction of the tread and aplurality of lateral grooves each extending across the circumferentialgrooves and tread ends, the improvement wherein each block in all blockrows is provided with a single fine groove extending in a widthwisedirection of the tread across the block, and the fine groove formed ineach block of an outermost block row is located in a leading edgeportion of the block and the fine groove formed in each block of theother block rows is located in a trailing edge portion of the block.